In the field of biophysics, biochemistry, biology, pharmacy, molecular diagnostics and analysis in general, samples are often exposed to different temperatures in order to characterize them according to their behavior at different temperatures.
For example, melting curve analyses, thermal stability measurements, “Thermal Shift Assays” (TFA) and Differential Scanning Fluorimetry (DSF) are important tools to qualitatively and quantitatively determine the stability and aggregation behavior of proteins and active agent formulations.
A further example is the MicroScale Thermophoresis (thermo-optical particle characterization), by means of which for examples affinities (Kd, EC50) of interactions at different temperatures are measured in order to derive the thermo-dynamic values dH and dS from the measurement results for example by means of a van't Hoff Plot.
In the field of biophysics, biochemistry, biology, pharmacy, molecular diagnostics and analysis (for example food analysis, cosmetics, . . . ) particularly aqueous solutions like buffers, lysates, urine, sera, whole blood etc. or liquids in general are used. In this respect, the temperature range to be examined extends from for example 0° C. to 100° C. or to the range in which the respective fluid is in its liquid form.
Capillaries as sample containers are of particular interest with respect to said applications since they have a particularly small and particularly well defined volume. Furthermore, capillaries may autonomously be filled with liquids by capillary forces, which makes for example the use of pumps superfluous. Furthermore, capillaries, for example made of borosilicate 3.3 quartz, synthetic fused silica, etc., are also advantageous with regard to their optical properties, in particular their transparency, purity and autofluorescence. In particular, short capillaries with a small inner diameter and a small outer diameter, for example an outer diameter of not more than 1 mm and an inner diameter of not more than 0.8 mm, preferably an outer diameter of 0.65 mm and an inner diameter of 0.5 mm, are advantageous since they only have a little volume and thus sample material can be saved.
In order to perform the described measurement methods, as for example a melting curve analysis, the capillaries have to be tempered, for example from 10° C. to 100° C. During said tempering, a high vaporization of the liquid at increased temperatures can typically be observed. Said vaporization or evaporation leads to disturbing currents in the liquid and in particular to such a high loss of liquid that measurements at increased temperatures over a longer time period are not possible.
Said vaporization may be avoided or reduced by for example sealing the ends of the capillaries with wax or by welding up the capillaries with a flame. However, said sealing methods involve significant disadvantages. Welding up the capillaries causes, in particular when quartz is used (which is advantageous for measurements with electromagnetic radiation in the UV range due to its good optical properties, in particular the low autofluorescence), such high temperatures that the molecules to be examined are changed or destroyed during welding and can thus no longer be examined. Furthermore, hardly any user has the necessary equipment to produce flames which are hot enough and defined enough to locally weld the ends of quartz capillaries in a defined manner.
Sealing the capillaries with an additional material, for example with wax, always contains the risk of contaminating the fluid/sample with the sealing material and thus to falsify the measurements. Further, it can be observed that sealings, as for example wax, may be pressed out of the capillary due to the vapor pressure in the capillary at increased temperatures and thus lose their functionality.
Systems in which capillaries are provided in the form of Micro Cuvette Arrays (MCA) are also known. Said Micro Cuvettes are put into a frame wherein said frame seals the cuvettes by means of silicon strips at both ends. In order to avoid contamination, said silicon strips and/or the frame have/has to be exchanged regularly, which causes additional costs.
However, since it is desirable with regard to biomolecules, for example proteins, peptides, nucleic acids, DNA, RNA, antibodies but also cells, bacteria, nanodiscs, vesicles, viruses etc. to work with very small volumina in the microliter range, short, very thin capillaries are advantageous. Furthermore, it is advantageous to use capillaries with thin walls, since for example autofluorescence and other artifacts may be minimized by said thin walls.
Thin capillaries with thin walls, i.e., capillaries with a small diameter and a thin wall, however, have the disadvantage of being very fragile. For that reason, the nondestructive, mechanical sealing of the capillaries, for example by a plug or a cap, is either not possible or only with significant effort which is thus no longer efficient.
Thus, there is the need of a simple or improved method by which optical measures may be carried out at increased temperatures also over a longer time period.